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STP Root Bridge is pointing at FWSM

Level 1
Level 1

Good afternoon all,

I have two 6509s both with single FWSMs running in transparent mode with bridged Inside and Outside VLANs.

I have my Core A set to STP priority of 8192 and Core B set to 16,384 to make Core A the root for all VLANs.

Problem I have is when I look at spanning-tree on Core A for Inside VLAN 324 it states to get to the Root go via PO100 (Cost of 9) and that the Root also has a Priority of 8192, but as the designated Root has a lower MAC address it's pointing to the etherchannel. PO100 is L2 Etherchannel between the Cores.

Moving accross PO100 to Core B and running the show spanning-tree command I can see that to get to the Root Bridge I need to go via PO272.  PO272 is the internal Etherchannel to get to the FWSM on the Core B Switch.  This shows a cost of 6 to get to the Root and a mac address of the Root Bridge which resides on Core A (Outside VLAN 124)

To give some perspectibe,theoutside VLAN of the pair has it's STP ROOT on the Core A switch as intended

Any help would be much appreciated


1 Reply 1

Hello David,

Can you try specifying the stp root via the primary/secondary commands - spanning-tree vlan xxx root primary/secondary. instead of specifying the priority value, this will decrease its own priority value if another switch challange's for stp root with it present priority vlaue.

Also you could  apply  spanning-tree rootguardto protect your root switch designated ports becoming root ports towards a new stp root switch

To influence a directly connected downstream switch from the root to elect its stp root port use  - spanning-tree vlan x port-priority x ( highest value less preferred)

To influence a local switch towards the root to elect its stp root port use   - spanning-tree vlan x cost y  ( highest value less preferred)

Welcome any other CSCr's to jump in here and correct me if i am wrong?



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